Selective fusing

ABSTRACT

Fuser regulating methods and the apparatus therefor are provided in accordance with the teachings of the present invention wherein a fuser assembly is selectively energized in accordance with the intermittent movement of successive portions of a support base through the fuser assembly such that said fuser assembly rapidly attains an operating temperature sufficient to fuse to said support base the electroscopic particles supported thereon. The fuser assembly is energized for a pre-established minimum period of time when successive portions of the support base are moved therethrough within a first time duration. The fuser assembly is energized for a second pre-established period of time greater than the minimum period of time when a first interval of time has expired since the immediately preceding energization thereof. If a second interval of time has expired since the immediately preceding energization of the fuser assembly, the assembly is energized for a third pre-established period of time when the next successive portion of the support base is advanced thereto. The second interval of time is greater than the first interval of time and the third pre-established period of time is greater than the second pre-established period of time. Further periods of energization may be established in accordance with the amount of time that has expired since an immediately preceding energization.

United States Patent [191 Hutner SELECTIVE FUSING [75] Inventor: Mark A.Hutner, GlenviewJll.

[73 Assignee: Xerox Corporation, Stamford, C on n. [22] Filed: Jan. 27,1972 [21] Appl. No.: 221,193

[52] US. Cl. 2l9/2l6,-2l9/388, 250/65 ZE [51] Int. Cl. B601 l/02 [58]Field of Search 219/216, 388; 250/65 Z5, 65 T [56] References CitedUNITED STATES PATENTS 3,398,259 8/1968 Tregay 2191388 X 3,505,497 4/1970Lawes et a1... 219/216 3,532,855 10/1970 Van Cleave 219/216 3,558,8531/1971 Schluntz 219/338 X 3,577,137 5/1971 Brennan, Jr. 219/2163,588,445 6/1971 Hopkins 219/216 X 3,628,860 12/1971 Ogawa 219/388 X3,684,372 8/1972 Limberger 219/216 X 3,697,722 10/1972 Furuichi et al.219/216 Primary ExaminerWilliam M Shoop, Jr. Att0rney,lames J. Ralabateet al.

[57] ABSTRACT Fuser regulating methods and the apparatus therefor ToScanning 8r Selection Circuit 11] 3,743,779 [451 July 3,1973

are provided in accordance with the teachings of the present inventionwherein a fuser assembly is selectively energizedin accordance with theintermittent movement of successive portions of a support base throughthe fuser assembly such that said fuser assembly rapidly attains anoperating temperature sufficient to-fuse to said support base theelectroscopic particles supported thereon. The fuser assembly isenergized for a pre-established minimum period of time when successiveportions of the support base are moved therethrough within a first timeduration. The fuser assembly is energized for a second pre-establishedperiod of time greater than the minimum period of time when a firstinterval of time has expired since the immediately precedingenergization thereof. If a second interval of time has expired since theimmediately preceding energization of the fuser assembly, the assemblyis energized for .a third pre-established period of time when the nextsuccessive portion of the support base is advanced thereto. The secondinterval of time is greater than the first interval of time and thethird pre-established period of time'is greater than the secondpre-established period of time. Further periods of energization may beestablished in accordance with the amount of time that has expired sincean immediately preceding energiza- 15 Claims, 5 Drawing Figures PatentedJuly 3, 1973 3 Sheets-Sheet 2 Patented July 3, 1973' 3 Sheets-Sheet 3 3woz 3w now z mo: $3 3.. 1oz

2- wow wow SELECTlVE FUSING This invention relates to electroscopicfusing techniques and, more particularly, to a method of selectivelyregulating a fuser assembly and the apparatus therefor.

Electrophotographic reproducing techniques of the type described indetail in U.S. Pat. No. 2,297,691 which issued to Chester F. Carlson,form electrostatic latent images of original documents by selectivelydissipating a uniform layer of electrostatic charges deposited on thesurface of a photo-receptor in accordance with modulated radiationimaged thereon. The electrostatic latent image thus formed is developedand transferred to a support surface to form a final copy of an originaldocument. The development process is effected by applying electroscopicparticles, conventionally known as toners, to the electrostatic latentimage whereat such particles are electrostatically attracted to thelatent image in proportion to the amount of charge comprising suchimage. Hence, the areas of small charge concentration are developed toform areas of low particle density, while areas of greater chargeconcentration are developed to form areas wherein the particle densityis greater. Once transferred to the support surface, the developed imagemay be permanently fixed thereto by heat fusing techniques wherein theindividual particles soften and coalesce when heated so as to readilyadhere to the support surface.

Various modifications in fusing techniques have heretofore beendeveloped which achieve divers results, such techniques includingselective fusing. ln selective fusing, toner areas admitting of a higherdensity are .preferentially fused leaving low density or backgroundareas unfused. Unfused toner particles comprising background can then beremoved to yield a cleaner, more readable copy. Selective fusing alsocontemplates the irregular, non-continuous, non-periodic operation of afuser assembly in response to particular predetermined conditions. Inthis regard, selective fusing techniques are readily adapted tocooperate with selective xerographic printing techniques. Thus, ifcopies of only selected ones of successively scanned original documentsare to be printed, the fuser assembly must be energized each time adeveloped image of a selected original is transferred to the supportsurface. It is appreciated that if the support surface comprises a webof suitable material, such as paper, the web will be transported throughthe fuser assembly in an irregular manner corresponding to the scanningof the unique originals to be reproduced. Consequently, scorching orburning of the web that is stationarily disposed within the fuserassembly must be avoided, while, at the same time, sufficient heat mustbe accummulated in the assembly to assure an adequate fusing of thetoner areas to the web.

In the implementation of either of the aforementioned selective fusingtechniques, i.e., the fusing of toner areas of a high density to theexclusion of relatively low density areas on a continuously movingsupport surface or the fixing of successive toner areas disposed inimage configuration upon an irregularly moving support surface, it hasbeen found, that in addition to the problem of scorching the supportsurface, it is necessary to provide for an intrinsic delay in raisingthe temperature of the fuser assembly to a proper value in response tothe energization thereof, the accumulation of heat within the assemblyduring the duration of energization thereof and the temperature to whichthe assembly has cooled in the time that has expired since theimmediately preceding energization thereof. An attendant disadvantage ofprior art selective fusing techniques is the failure of such techniquesto vary the amount of heat emitted by the fuser assembly in accordancewith the length of time such assembly has been permitted to cool. Anattempt to overcome this difficulty has resulted in maintaining thefuser assembly at a quiescent temperature level that, in some instances,has caused the scorching of the support surface disposed therein.

Therefore, it is an object of the present invention to provide a methodof and apparatus for selectively fusing electroscopic particles to asupport surface.

It is another object of the invention to provide a method of andapparatus for regulating the operation of a fuser assembly in accordancewith selected conditions requiring the energization of said assemblywherein the heat accumulated by the assembly is a function of theexpiration of time from an immediately preceding energization thereof.

A further object of the present invention is to provide a method offusing electroscopic particles to'successive portions of a support baseintermittently moving through a fuser assembly, and the apparatustherefor.

An additional object of the present invention is to provide apparatusfor selectively energizing a heating element that is maintained at atemperature level no lower than a quiescent level for variable timedurations such that a substantially equal radiant energy level isattained thereby during each energization irrespective of the length oftime that has expired since an immediately preceding energizationthereof.

Still another object of this invention is to provide a method of rapidlyenergizing a fuser assembly to permit the fixing of toner particlesthereby, while precluding the possibility of scorching a support surfacedisposed therein, and the apparatus therefor.

Yet a further object of the present invention is to provide a method ofselectively energizing a fuser assembly, and the apparatus therefor, inaccordance with the amount of cooling to which said assembly has beensubjected.

Another object of this invention is to provide a method of and apparatusfor fusing electroscopic particles disposed in image configuration on asupport surface in accordance with the intermittent movement of saidsurface through a fuser assembly.

Various other objects and advantages of the invention will become clearfrom the following detailed description of an exemplary embodimentthereof, and the novel features will be particularly pointed out inconnection with the appended claims.

In accordance with this invention, there are disclosed fuser regulatingmethods and the apparatus therefor, wherein the fuser assembly isselectively energized in accordance with the occurrence of preselectedconditions such that the fuser assembly rapidly attains an operatingenergy level sufficient to fuse to a support surface the electroscopicparticles supported thereon; said fuser assembly being energized for apreestablished minimum duration of time when the immediately precedingenergization thereof occurred within a first time duration; and saidfuser assembly being energized for variable durations of time inaccordance with the interval that has expired since the immediatelypreceding energization thereof. 1

The invention will be more clearly understood by reference to thefollowing detailed description of an exemplary embodiment thereof inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a typical selective printing apparatuswith which the instant invention may be utilized;

FIG. 2A is a schematic diagram of a conventional heating element thatmay be utilized in the fuser assembly of P16. 1 and variable supply ofenergy therefor;

FIG. 2B depicts an AC waveform that is helpful in explaining theoperation of the electrical circuit illustrated in FIG. 2A;

FIG. 3 is a schematic illustration of the logic circuitry that may beutilized to selectively regulate the variable supply of energy depictedin FIG. 2A; and

FIG. 4 depicts a timing diagram representing the voltage signalsproduced by the logic circuit of FIG. 3.

For a general understanding of selective printing apparatus in which theinstant invention may be incorporated, reference is made to FIG. 1 inwhich some of the various system components for the apparatus areschematically illustrated. Like component parts are identified by likereference numerals throughout and primed reference numerals identify thewaveforms produced by corresponding component parts identified byunprimed reference numerals. The printing apparatus illustrated hereinemploys electrophotographic concepts originally disclosed in US. Pat.No. 2,297,691, which issued to Chester F. Carlson. Accordingly, theselective printing apparatus comprises an electrostatic system wherein alight image of an original to be reproduced is projected onto thesensitized surface of a photosensitive plate to form an electrostaticlatent image thereon. Thereafter, the latent image is developed with anoppositely charged developing material comprising electroscopicparticles, known as toner particles, to form a powder imagecorresponding to the latent image on the photosensitive surface. Thepowder image is then electrostatically transferred to a support base towhich it may be fixed by a fusing assembly whereby the powder is causedto adhere permanently to the support surface.

In the illustrated apparatus, visible document information is providedon each of the data cards 1 that are successively transported from afeeder tray 2 to a restack tray 49. The data cards are transported intimed sequence with respect to the operationof the remaining apparatusillustrated herein, and are caused to traverse detecting station A,scanning station B and slit exposure device 34 in successive order. Eachdata card is additionally provided with precoded information thereon,which precoded information is determinative of the selective printing ofthe visible document information carried by the card. More particularly,if the precoded information scanned from the card by canning'station Badmits of a particular precondition, additional logic circuitry, notshown, responds to such scanned information to derive a print signal.The thus derived print signal is operated upon in a timed sequence toprovide a direct correspondence between the sequential manipulation ofsuch print signal and the particular operation performed by theapparatus illustrated in FIG. 1.

The sequential passage of data cards from the scanning station B throughthe projection system 33 to the restack tray 49 will cause opticalimages of the visible document information on each of the data cardspassing through the slit exposure device 34 to be sequen- 1 tiallyprojected upon the surface of photosensitive drum 20. If desired, theprojected images may admit of magnification. The photosensitive drum 20is continuously driven at a constant angular velocity such that thesurface thereof is moving at a velocity equal to that of the data cardsmoving past the exposure device .34. In moving in the directionindicated by the arrow, prior to reaching the exposure station C, thatportion of the image configuration corresponding to the light imageprojected from the visible document information on the data cardtransported through the slit exposure device 34. As the photosensitivedrum surface continues its movement, the electrostatic image passesthrough a developing station D in which there is positioned a developingapparatus generally indidicated by the reference numeral 13.

If the electrostatic latent image passing through development station Dis derived from a data card having a print signal associated therewith,such print signal is utilized to activate the developer motor 24 suchthat the developing apparatus may be operated to develop suchelectrostatic latent image. In contradistinction thereto, should theelectrostatic latent image passing through the developing station D bederived from a data card not having a print signal associated therewith,the developer motor 24 is not activated and such electrostatic latentimage is not developed. It is therefore appreciated that the developingapparatus 13 is operated in an intermittent manner wherein only thoseelectrostatic latent images derived from data cards having print signalsassociated therewith are developed at station D. Hence, as thephotosensitive drum 20 continues to rotate in the direction indicated bythe arrow, successive areas thereof will be provided with imageinformation distributed thereon in the form of a distributedelectrostatic charge pattern. However, only selected ones of successiveareas will be developed. As illustrated herein, the developing apparatus13 may typically be provided with electroscopic particles that arecascaded across the surface of photosensitive drum 20, which particlesare attracted electrostatically to the distributed charge pattern toform powder images.

The developed electrostatic image is transported by the photosensitivedrum 20 to a transfer station E located at a point of tangency on thephotosensitive drum whereat a support base 9 is intermittently moved ata speed in synchronism with the moving drum in order to accomplishtransfer of the developed image. The support base 9 is here depicted asa web comprised of suitable material such as paper, plastic or the like,that is driven from a supply 13 through selective transfer mechanism 25,through fuser assembly 40, about strip driving means 16 and into a stripreceiving tray 14. At the time a developed image having a print signalassociated therewith arrives at the transfer station E, the associatedprint signal is operated upon to cause the web driving means 16 to beactivated, thereby transporting the support base 9 at a velocity equalto the surface velocity of the photosensitive drum 20. Moreover, theprint signal is used to operate the selective transfer mechanism wherebythe support base 9 engages the photosensitive drum 20 in an arc ofcontact. In addition, charging means may be energized to provide acharge on the support base 9 prior to its engagement with thephotosensitive drum so that the developed image may be electrostaticallytransferred from the surface of drum 20 to the adjacent side of thesupport base as such support base is brought into contact therewith.Thus, it is seen, that each developed electrostatic image is transferredto the support base 9; and the support base is, therefore, advanced inan intermittent manner in accordance with each print signal that isderived from the scanning information carried by the transported datacards.

After transfer, the support base 9 is transported to the fuser assembly,generally indicated by the reference numeral 40, wherein the developedand transferred powder image on the support base is permanently fixedthereto. The fuser assembly 40 may comprise conventional apparatuscapable of carrying out various fusing techniques such as oven fusing,hot air fusing, radiant fusing, hot and cold pressure roll fixing andfusing and flash fusing. Merely for the purpose of explanation, it willbe assumed that the fuser assembly 40 is comprised of one or more quartzlamps connected in parallel relationship and adapted to emit a suitableamount of heat when energized. The dimensions of the assembly may besuch as to admit of a plurality of transferred images to be disposedtherein. Additionally, the fuser assembly is maintained at a quiescentoperating temperature when not energized, said quiescent operatingtemperature being slightly less than the temperature normally requiredto fix the powder image to prevent scorching of the support base. It is,therefore, readily apparent that the print signal derived from a datacard is operated upon in a preselected sequential manner incorrespondence with the transporting of a transferred image to the fuserassembly 40. Since, however, immediately succeeding areas of the supportbase 9 are provided with transferred images, but succeeding ones of thedata cards are not necessarily provided with the unique precodedscanning information, it is recognized that the support base is movedintermittently through the fuser assembly inan irregular manner.Consequently, the fuser assembly must not be continuously energized inorder to avoid the scorching of the support base that is maintained in atemporary stationary relationship with respect thereto. Nevertheless, asan immediately succeeding portion of the support base is advanced to thefuser assembly, the latter must be rapidly energized to an operatinglevel capable of fixing the electroscopic powder image upon the supportbase. The manner in which the fuser assembly 40 is regulated to providethe just-mentioned selective fusing is described in detail hereinbelow.

The excess electroscopic particles remaining as residue on the developedimages, .as well as those particles not otherwise transferred therefrom,are carried by the photosensitive drum 20 to a cleaning station F on theperiphery of the drum adjacent the charging station G. The cleaningstation may comprise a rotating brush and a corona discharge device forneutralizing charges remaining on the nontransferred electroscopicparticles. Various other configurations and components may comprise thecleaning station F as is well-known to those of oridinary skill in theart.

A more complete description of the selective printing apparatusillustrated in FIG. 1, and the manner in which such apparatus operates,is set forth in detail in copending application, Ser. No. 221,229 filedon Jan. 27, 1972 by Mark A. I-Iutner et al, and now U.S.- Pat. No.3,700,324 and assigned to Xerox Corporation, the assignee of the instantinvention. It should, however, be clearly understood that the selectivefusing techniques to be described in detail hereinbelow are readilyadapted for broad application and should not be unnecessarily limited tothe specific system described above. It will, therefore, become readilyapparent that the instant invention may be readily utilized wheneverselected ones of original documents are to be reproduced. Statedotherwise, the selective fusing techniques described hereinbelow arereadily adapted to fix powder images to a support base therefor on anirregular basis in accordance with the occurrence of preselectedconditions. Thus, in addition to the selected use as described withrespect to FIG. 1, the selective fusing techniques of the presentinvention may be employed for the preferential fusing of dense imageareas while leaving low density or background areas unfused.

Turning now to the subject matter of the present invention, and inparticular, to FIGS. 2A and 28, there is schematically illustrated aconventional heating element 105 that may be typically included in thefuser assembly 40 of FIG. 1. The heating element 105, which may comprisea plurality of quartz lamps connected in parallel relationship, iscoupled to a variable supply of voltage, generally designated by thereference numeral 100, the latter being adapted to supply the heatingelement 105 with energy. The variable supply may be a conventionalvoltage regulator such as model 9T68Y700l manufactured by GeneralElectric, and therefore need not be described in detail herein. Itshould however, be noted that the variable supply 100 includesbi-directional current conducting means 101 which may be a siliconbi-directional triode device, such as a triac, capable of conductingrelatively high AC current in both directions and whose time of initialconduction during a half cycle is dependent upon the magnitude of a.control'voltage applied to the trigger input 101a thereof. Hence, thebi-directional current conducting means 101 may function as atriggerable switch that is rendered conductive during a half cycle of anAC voltage applied thereto when the voltage exceeds a threshold orfiring level. Those of ordinary skill in the art will recognize that thebi-directional current conducting means may be a conventional thyrister.Once rendered conductive, the bi-directional current conducting means101 is adpated to remain conductive until tthe voltage applied theretocommences a successive half cycle.

It may be observed that the control voltage applied to the trigger input101a of bi-directional current conducting means 101 is derived from avoltage dividing means that comprises series connected resistance means102, 103 and 104. Trigger input 101a is coupled to the junction formedby the series connection of resistance means 102 and 103. The value ofthe resistance of resistance means 102 is, to some degree, determined bythe intensity of radiant energy emitted by lamp 108 and, therefore, isprecisely regulated. In accordance with the present invention, thethreshold level at which the bi-directional current conducting means 101is rendered conductive, is decreased by selectively reducing the voltagederived by the illustrated voltage dividing means. Adjustable resistancemeans 106 is capable of being selectively connected in parallelrelationship with resistance means 102 by energizable switch 107. Itshould be appreciated that the effective resistance of the first stageof the illustrated voltage dividing means is decreased when adjustableresistance means 106 is connected in parallel with resistance means 102.Consequently, the threshold or firing level voltage applied to thetrigger input 101a of bi-directional current conducting means 101 iscorrespondingly increased. Thus, the time of initial conduction during ahalf cycle is advanced and the duration of conductivity of thebidirectional current conducting means 101 is increased. With adjustableresistance means 106 connected in parallel with resistance means 102,the root mean square (RMS) voltage applied to heating element 105 isdecreased, resulting in a decrease in the amount of heat radiatedtherefrom. Adjustable resistance means 106 may comprise a conventionalpotentiometer, rheostator the like whereby an adjustment of theresistance value thereof enables a corresponding adjustment in thethreshold or firing level of bidirectional current conducting means.Hence, a suitably wide range in the RMS voltage applied to heatingelement 105 may be obtained.

The manner in which the variable supply 100 is utilized to regulate theheat radiated by heating element 105 may be readily understood byreferring to FIG. 2B. Normally, the heating element 105 is maintained ata quiescent level of energization to radiate an amount of heat that isnot quite sufficient to fuse electroscopic material to a support base.Nevertheless, this quiescent energization enables the radiant energyemitted by the heating element to be rapidly increased to aproper-fusing level when the voltage applied to said heating element isincreased. When adjustable resistance means 106 is connected in parallelwith resistance means 102, a quiescent threshold level is applied totrigger input 101a of bi-directional current conducting means 101. Asillustrated in FIG. 28, this quiescent threshold level renders thebi-directional current conducting means conductive at a point on thepositive half cycle of the AC voltage applied to the bi-directionalcurrent conducting means defined by the intersection of broken line 121aand AC waveform 120. The bi-directional current conducting means 101 isrendered nonconductive at the conclusion of a positive half cycle.However, at a point on the negative half cycle defined by theintersection of broken line 121k and AC waveform 120, the bi-directionalcurrent conducting means is again rendered conductive. It is appreciatedthat when the quiescent thershold level is applied to trigger input 1010of bi-directional current conducting means 101, the bi-directionalcurrent conducting means is rendered conductive for only a relativelysmall portion of an AC cycle. This duration of conductivity, however issufficient to apply an RMS voltage to heating element 105 whereby theheating element is maintained at a quiescent level of energization.Should the RMS voltage applied to heating element 105 be increased, the

heat radiated thereby will be sufficient to fuse electroscopic material.

When energizable switch means is energized so as to assume an open"state, adjustable resistance means 106 is thereby disconnected fromresistance means 102. It may be recognized that switch means 107 maycomprise the movable contact of a conventional relay, an electronicswitch or the like. The disconnecting of adjustable resistance means 106from resistance means 102 alters the ratio of division of the voltagedividing means to thereby alter the threshold level applied to triggerinput 101a. Accordingly, the point at which the bi-directional currentconducting means 101 is rendered conductive during the positive halfcycle of the AC voltage applied thereto is defined by the intersectionof line 122a and AC waveform 120 illustrated in FIG. 2B. Theconductivity of the bi-directional current conducting means ismaintained until the conclusion of the positive half cycle. During thenegative half cycle of the AC voltage, bi-directional current conductingmeans 101 is rendered conductive at the point of intersection of line1221) and AC waveform 120. The relatively large duration of conductivityduring each cycle is effective to apply an increased RMS voltage toheating element 105 whereby the heat radiated by the heating element issufficient to fuse the electroscopic material. It should be readilyunderstood that if energizable switch means 107 is energized for aplurality of AC cycles, the amount of heat radiated by heating element105 is proportionally increased. Therefore, the total amount of heatradiated by the heatingelement and, consequently, the increase intemperature obtained thereby, is a function of the duration ofenergization of energizable switch means 107. 7

An exemplary embodiment of apparatus that may be utilized to energizeenergizable switch means 107 is schematically illustrated by the logiccircuit of FIG. 3 and comprises storage means 200, gating means 203, 204and 206, selective gating means 209 and driver means 211. Storage means200 is adapted to store a history of the preceding energizations of'theheating element included in the fuser assembly 40 illustrated in FIG. 1and, therefore, may comprise a plural stage shift register meansincluding an input terminal for receiving an irregularly occurringselective energizing signal and a shift terminal for receiving aperiodic shift signal. It is recalled that the selective printingapparatus with which the present invention may be utilized is adapted todevelop and transfer an image of a given data card when said card isprovided with scanning, information from which is derived a printsignal. As described in copending application Ser. No. 221,229 filedJan. 27, 1972, and now us. Pat. No. 3,700,324 a derived print signal isshifted through shift register means in timed relation with the rotationof image information obtained from a corresponding-data card. The imageinformation is distributed on the surface of a rotatingphotosensitivedrum in the form of a distributed electrostatic chargepattern. Accordingly, the relative position of the image information atany given time may be determined by the particular position occupied bythe print signal as said print signal is shifted through the shiftregister means. Moreover, once the image information is developed andtransferred to a portion of the support base, the movement of thatportion may be represented by a corresponding shifting of the printsignal through the shift register means. It should, therefore, bereadily apparent that a print signal will be shifted to a predeterminedposition within the shift register means when a portion of the supportbase is advanced to the fuser assembly. Hence, electroscopic 9 particlesthat are disposed in image configuration on the support base are to befused to the support base when a print signal occupies saidpredetermined position. As will soon become apparent, the print signaloccupying the predetermined position need not be associated with thatparticular portion of the support base that is advanced to the fuserassembly. However, except for initial portions of the support base, eachsucceeding portion that is transported to the fuser has a powder imagedisposed thereon. Storage means 200 may, therefore, comprise a portionof the aforementioned shift register means having a first stagecorresponding to .the predetermined position and including a pluralityof succeeding stages. Alternatively, the storage means 200 may comprisean individual plural stage shift register means having a first stagecorresponding to the aforementioned predetermined position and includinga plurality of succeeding stages. In either case, the storage means isillustrated in FIG. 3 as comprising a plural stage shift register meanswherein only stages 1-8 have been designated as only these stages are ofinterest here. As is understood by those of ordinary skill in the art, aconventional shift register is adapted to shift an input signal appliedthereto consecutively through the stages thereof in accordance with atransition in the shift signal applied. The shift register may,therefore, comprise a counter capable of representing timing informationrelating to the times of occurrence of successive input signals inaccordance with the particular stages occupied thereby.

The input terminal of storage means 200 is coupled to terminal 201 towhich is applied a preselected information signal such as theaforementioned print signal. The shift terminal of storage means 200 iscoupled to terminal 202 to which is applied a periodic shift signal. Theperiodic shift signal may be derived from the system clock which isexplained in detail in copending application Ser. No. 221,229 filed Jan.27, 1972 and now U.S. Pat. No. 3,700,324. Accordingly, the periodicshift signal may take the form of clock pulses having a periodcorresponding to the rate at which the data cards are scanned andimaged. The clock pulse period is thus equal to the interval of timerequired to transfer successive developed images from the photosensitivedrum to support base 9. Consequently, the clock pulse period is alsoequal to the interval of time required to translate successive portionsof the support base 9 to the fuser assembly 40.

The outputs of stages 1-8 of storage means 200 are coupled to theillustrated decoding means, which de coding meansis adapted to analyzethe sequence of the print signals that have been supplied to storagemeans 200. The decoding means includes first gating means 203, secondgating means 204, third gating means 206 and selective gating means 209.First gating means 203 is comprised of a coincidence means including afirst input terminal coupled to the first stage of storage means 200 anda second input terminal coupled to terminal 202. Coincidence means 203is adapted to produce a signal admitting of a pre-established minimumduration whenever a print signal is applied to terminal 201. It isappreciated, therefore, that the coincidence means is adapted to producean output signal in response to the application of a predeterminedsignal at each input terminal thereof. Accordingly, coincidence means203 may comprise a conventional AND gate whereby a binary l is producedat the output terminal thereof when a binary l is supplied to each inputterminal thereof. For the purpose of the present discussion, it will beassumed that a binary l is represented by a positive DC potential and abinary 0 is represented by ground potential. It is, of course,understood that the foregoing binary signals may be represented by anysuitable voltage potentials. Similarly, coincidence means 203 maycomprise a conventional NAND gate whereby a binary 0" is produced at anoutput terminal thereof when a binary I is supplied to each inputterminal thereof.

The second gating means 204 is'adapted to sense the expiration of afirst interval of time intermediate successive occurrences of a printsignal and to produce a signal admitting of a second pre-establishedduration in response thereto. The second pre-established duration isgreater than the aformentioned pre-established minimum duration. Moreparticularly, gating means 204 is adapted to detect when more than twoclock pulse periods have expired since the occurrence of the immediatelypreceding print signal. Such expiration corresponds to an elapsed timesince the previous energization of the heating element included in fuserassembly 40 that the fuser assembly has cooled to a temperaturerequiring an energization thereof for a duration longer than the minimumduration to attain a suitable accumulation of radiant energy in theassembly. Second gating means 204 includes a first input terminalcoupled to a given stage, such as the first stage, of storage means 200via inverting means 205, a second input terminal coupled to a secondstage of storage means 200 and a third input terminal coupled to a thirdstage of storage means 200. An output signal is produced by secondgating means 204 when the first stage of storage means 200 is occupiedby a print signal but the second and third stages, respectively, ofstorage means 200 are not occupied by a print signal. Accordingly,second gating means 204 may comprise a conventional inverting OR, orNOR, circuit wherein a binary l is produced at the output terminalthereof when a binary 0" is applied to each input terminal thereof.Alternatively, the second gating means 204 may comprise a conventionalAND gate, similar to the aforedescribed AND gate 203, wherein a firstinput terminal thereof is coupled directly to the first stage of storagemeans 200 and the second and third input terminals thereof are coupledto the second and third stages, respectively, of storage means 200 viainverting means. The inverting means 205 illustrated herein may comprisea conventional logic negation circuit adapted to produce a binary 0" inresponse to a binary l supplied thereto, and, conversely, to produce abinary l in response to a binary 0 supplied thereto.

The third gating means 206 is adapted to sense the expiration of asecond interval of time intermediate successive occurrences of the printsignal, the second interval being greater than the aforementioned firstinterval. More particularly, gating means 206 is adapted to detect whenmore than six clock pulse periods have expired since the occurrence ofthe immediately preceding print signal. Should this condition obtain, itis appreciated that the time that has elapsed since the previousenergization of the heating element included in the fuser assembly 40 issufficient to permit cooling of the fuser assembly to a point whereat anextended energization thereof is preferred to achieve a suitableaccumulation of radiant energy therein. It will soon become readilyapparent that the condition precedent to the activation of gating means204 comprises a portion of the conditions precedent to the activation ofgating means 206. Hence, gating means 204 is adapted to produce a signalwhenever the gating means 206 produces a signal. This fact enables asimplification in the construction and interconnection of gating means206 such that the gating means may include a first input terminalcoupled to the second stage of storage means 200 via inverting means207, second through seventh input terminals coupled to stages 3-8,respectively, of storage means 200 and an eighth input terminal coupledto terminal 202 via inverting means 208. The gating means may comprise aconventional inverting OR, or NOR, circuit similar to NOR circuit 204or, alternatively, an AND gate similar to the AND gate previouslydescribed with respect to gating means 204. It is recog-. nized that ifgating means 206 is constructed of commercially available logiccomponents, an eight-input NOR circuit might not be feasible.Accordingly, the NOR circuit may be comprised of a pair of readilyavailable four-input NOR circuits having output terminals coupled to aconventional AND gate.

Although not specifically illustrated herein, additional gating means,similar to those just described, may be provided to sense the expirationof other intervals of time intermediate the successive occurrences of aprint signal. Similarly, the interconnections between gating means 206and storage means 200 may adopt any suitable configuration to permit thesensing of the expiration of any corresponding interval of time.

The output terminals of AND gate'203, NOR circuit 204 and NOR circuit206 are coupled to corresponding input terminals of the selective gatingmeans comprised of series connected inverting OR, or NOR, circuit 209and inverting means 210. It is recognized by those of ordinary skill inthe art that the combination of NOR circuit 209 and inverting means 210comprises a conventional OR circuit wherein a binary l isproduced at theoutput terminal thereof in response to the application of a binary l toany of the input terminals thereof. The OR circuit comprised of NORcircuit 209 and inverting means 210 is connected to conventional drivingmeans 211 which, in turn, is coupled to the energizing coil 212 of aconventional relay. Driving means 211 is adapted to respond to a switchenergizing signal applied thereto to supply the energizing coil 212 withground potential. Accordingly, driving means 211 may comprise aconventional transistor means having a base electrode coupled to the ORcircuit comprised of NOR circuit 209 and inverting means 210, acollector electrode coupled to the energizing coil 212 and an emitterelectrode coupled to ground potential. The OR circuit comprised of NORcircuit 209 and inverting means 210 is adapted to selectively couple thesignal admitting of pre-established minimumduration from AND gate 203 todrive means 211, the signal admitting of a second pre-establishedduration from NOR .circuit 204 to drive-means 211 and the signalproduced by NOR circuit 206 to drive means. 211. The OR circuit actsto'combine the signals produced by NOR circuits 204 and 206 to couple asignal admitting of a third preestablished duration to drive means 211.It is, of course, now apparent that the OR circuit is capable ofcoupling the signals produced by such additional gates that may beprovided to drive means 211.

The operation of the apparatus illustrated in FIG. 3 will now bedescribed. It is recalled that the successive portions of the supportbase 9 upon which the electroscopic particles are disposed in imageconfiguration are intermittently moved through the fuser assembly 40even though the data cards and photosensitive drum are continuallyadvanced and rotated, respectively. Consequently, it is expected that ifone out of five data cards, for example, are to be printed, only oneprint receiving portion of the support base 9 will be moved through thefuser assembly 40 during the interval required to process the five datacards. Stated otherwise, only one print'signal in the form of a pulsewill be applied to terminal 201 notwithstanding the application of fiveclock pulses to terminal 202. To facilitate the ready understanding ofthe instant invention, the example represented by the timing diagram ofFIG. 4, as read in a left to right configuration, will be assumed. Thisexample is assumed merely for purposes of illustration and should not beconsidered to unnecessarily limit the instant teachings of the inventionthereto. It will also be assumed that the fuser assembly and printingapparatus operatively associated therewith has been in operation forsome time. At the first timing period under consideration, i.e., attiming pulse 1 of waveform 202', the first print signal, represented bythe first pulse at the left-hand portion of waveform 201 is applied toterminal 201. It is seen that this first pulse 201 represents that aportion of the support base 9 has been advanced to the fuser assembly40, the heating el ement included in the fuser assembly must now beenergized to attain a temperature sufficient to achieve the fixing ofthe electroscopic particles to the support base and the heating elementhas not been energized since the last occurrence of the immediatelypreceding pulse 201', not shown. Thus, at clock pulse 1, the printsignal is shifted into the first stage of storage means 200 and stages2-8 thereof are not provided with print signals. The storage means 200may be responsive to the positive transition of the clock pulses 202'applied thereto. Of course, the negative transitions of the clock pulsesmay be utilized to shift applied signals through the storage means, ifso desired. Accordingly, AND gate 203 is supplied with a binary 1 by thefirst stage of storage means 200 and with a binary l by clock pulse 1applied to tenninal 202 to produce a first energizing signal admittingof a duration equal to the duration of clock pulse 1 as illustrated bywaveform 203. Similarly, NOR circuit 204 is supplied with a binary 0"bythe second and third stages, respectively, of storage means 200 and,after the invention of the binary l' stored in the first stage ofstorage means 200, with a binary 0 by inverting means 205 to produce anenergizing signal admitting of a duration equal to the clock pulseperiod, as represented by waveform 204'. It is apparent that theenergizing signal produced by NOR circuit 204 represents that more thantwo clock pulse periods have expired since the occurrence oftheimmediately preceding print signal. Thus, at clock pulse 1, the

OR circuit comprised of NOR circuit 209 and inverting means 210 respondsto the energizing signals applied thereto by AND gate 203 and NORcircuit 204 to supply driver means 211 with a switch energizing signaladmitting of a duration corresponding to that exhibited by waveform204'. This switch energizing signal, represented by waveform 210' andaligned with clock pulse 1, activates driver means 211 which, in turn,energizes the energizing coil 212 for a period of time equal to oneclock pulse period. Hence, during this period, current flows from thesource of energizing potential +V through energizing coil 212 to groundpotential applied to the energizing coil by driver means 211.Consequently, switch means 107 of FIG. 2A is activated and therebyopened, for a corresponding period of time. For the purpose ofillustration, it will be assumed that one clock pulse period admits of aduration equal to approximately 332 milliseconds, the width of a clockpulse is approximately 230 milliseconds and the frequency of the ACwaveform 120 illustrated in FIG. 2B is approximately 60hz. Theactivation of switch means 107 for a duration of approximately 332milliseconds will enable bi-directional current conducting means 101 tooperate upon approximately 20 cycles of the AC voltage applied theretoto supply heating element 105 with a sufficiently high RMS voltage. Theelectroscopic particles disposed in image configuration upon the supportbase 9 will, therefore, be fused thereto. However, since the fuserassembly 40 had not been previously energized for a prolonged period oftime, the heating element therein has cooled to a lower quiescenttemperature. It is, therefore, preferred that the heating element beenergized for a further duration to permit the fuser assembly toaccumulate additional radiant energy whereby a higher temperature isattained. Accordingly, at clock pulse 2, the print signal stored in thefirst stage of storage means 200 is shifted into the second stagethereof. This print signal pulse is inverted by inverting means 207 andthe first seven input terminals of NOR circuit 206 are each suppliedwith a binary Clock pulse 2 is inverted by inverting means 208 and theeighth input terminal of NOR circuit 206 is also supplied with a binary0. The signal thus produced by NOR circuit 206, depicted by the waveform206' in alignment with clock pulse 2, admits of a duration equal to theclock pulse duration and is applied to driver means 211. It isrecognized that the signal produced by NOR circuit 206 represents thatmore than six clock pulse periods have expired since the occurrence ofthe immediately preceding print signal. Switch means 107 is thusactivated for an additional 230 milliseconds (the approximate clockpulse duration) during the immediately succeeding clock pulse period. Itmay thus be observed that the switch energizing signal produced by theOR circuit comprised of NOR circuit 209 and inverting means 210, andrepresented by the waveform 210' is effective to energize the heatingelement of the fuser assembly for one complete clock pulse period andfor one additional clock pulse duration.

It is apparent from waveform 201', that at clock pulse 2 a print signalis not applied to terminal 201. Hence, the next successive portion ofthe support base 9 is not moved through the fuser assembly 40. This, ofcourse, means that the image information derived from the data cardcorresponding to clock pulse 2 is not to be printed. Nevertheless, itshould be noted that the additional energization of the heating elementof the fuser assembly during the second clock pulse period, as justdescribed hereinabove, is not sufficient to scorch or otherwise damagethe support base that extends within the fuser assembly. Moreover, ifthe support base has been advanced at clock pulse 2, the additionalenergization of the heating element would be advantageously utilized tofix the next successive developed image to the support base. At clockpulse 3, terminal 201 is not provided with a print signal and,therefore, the fuser assembly 40 need not be energized. In addition, atthis time, the first print signal that had been applied to terminal 201is shifted into the third stage of storage means 200. Similarly, atclock pulse 4, that print signal is shifted into the fourth stage ofstorage means 200.

Waveform 201' indicates that the next successive print signal pulse isapplied to terminal 201 during clock pulse period 5. At this time, theimmediately preceding print signal is shifted into the fifth stage ofstorage means 200. Hence, approximately 1,328 milliseconds (i.e., fourclock pulse periods) have elapsed since a given portion of the supportbase 9 was moved into the fuser assembly 40. Moreover, approximately 766milliseconds have elapsed since the energization of the heating elementof the fuser assembly 40 was terminated. The fuser assembly has,therefore, cooled such that the accumulated energy therein hasdissipated below the fusing level. At clock pulse 5, AND gate 203produces a signal illustrated by waveform 203', which signal is appliedto the OR circuit comprised of NOR circuit 209 and inverting means 210.In addition, NOR circuit 204 responds to each binary 0 applied theretoby the second and third stages, respectively, of storage means 200 andto the binary 0 applied thereto by inverting means 205. It is, ofcourse, appreciated that the print signal occupying the first stage ofstorage means 200 is subjected to a logic negation by inverting means205 to produce the last mentioned binary 0. Accordingly, a signalrepresented by the waveform 204 and admitting of a duration equal to aclock pulse period is also applied to the OR circuit comprised of NORcircuit 209 and inverting means 210. Consequently, at clock pulse 5, theswitch energizing signal, represented by waveform 210' is applied todriver means 211 whereby switch means 107 is activated. The activationof switch means 107 results in the energization of the heating elementincluded in the fuser assembly 40 for a duration equal to one clockpulse period. The electroscopic particles disposed on the support base 9in image configuration are thus fused to the support base. Furthermore,the energizing duration of approximately 332 milliseconds is sufficientto enable the fuser assembly to attain a desirably high temperature,thus accumulating an adequate amount of radiant energy.

A print signal is not applied to terminal 201 at the next clock pulseperiod 6 and, therefore, further movement of the support base 9 isinterrupted. Thus, that portion of the support base that was previouslyadvanced into the fuser assembly 40 remains therein and the accumulatedradiant energy serves to properly complete the fusing operation. Inaddition, at clock pulse 6, a binary 0 is shifted into the first stageof storage means 200 and the previous print signal is shifted into thesecond stage of storage means 200. Accordingly, AND gate 203 and NORcircuit 204 are each disabled and thus do not produce output signals.Although the print signal stored in the second stage of storage means200 is inverted by inverting means 207 and applied as a binary 0 to NORcircuit 206, it is observed that the first print signal has now beenshifted to the sixth stage of storage means 200 and, therefore, NORcircuit 206 is also disabled from producing a pulse signal. This, ofcourse, is expected since not more than six clock pulse periods haveelapsed intermediate the first and second print signal times ofoccurrence.

The next succeeding print signal is applied to terminal 201 at clockpulse 8 and is shifted into the first stage of storage means 200 asindicated by the waveform 201. Hence, three clock pulse periods haveelapsed since the immediately preceding print signal was applied toterminal 201 and approximately 664 milliseconds have elapsed since theenergization of the heating element included in the fuser assembly wasterminated. At clock pulse 8, the immediately preceding print signal isshifted into the fourth stage of storage means 200 and the first printsignal is shifted into the eighth stage of storage means 200.Accordingly, AND gate 203 responds to the print signal applied to itsfirst input terminal and to the clock pulse applied to its second inputterminal to produce the signal represented'by waveform 203' admitting ofa clock pulse duration. Additionally, the elapsed time betweensuccessive print signals exceeds two clock pulse periods and NOR circuit204 responds to each binary 0 applied thereto by inverting means 205 toproduce the signal represented by the waveform 204' admitting of aduration equal to the clock pulse period. NOR circuit 206 is inhibitedfrom producing an output because the first print signal is applied to aninput terminal thereof by the eighth stage of storage means 200. The ORcircuit comprised of NOR circuit 209 and inverting means 210 responds tothe signals applied thereto by AND gate 203 and NOR circuit 204 to applya switch energizing signal represented by the waveform 210' to drivermeans 211. Switch means 107 is, therefore, activated for a durationequal to a clock pulse period, thereby energizing the heating element105 included in the fuser assembly 40. Consequently, the eleetroscopicparticles disposed in configuration upon the third successive portion ofthe support base 9 are fused thereto.

At clock pulse 9 an immediately succeeding print signal is applied toterminal 201, thereby representing that the support base 9 is advancedthrough fuser assembly 40 to expose the next successive portion of thesupport base to a fusing operation. It is, therefore, appreciated thatthe image information derived from consecutive data cards are to beprinted. Hence, at clock pulse 9 the i first and second stages ofstorage means 200 are each occupied by a print signal, the fifth stageof storage means 200 is occupied by a print signal and the remainingstages of storage means 200 are not provided with print signals. It is,therefore, appreciated that only AND gate 203 is activated to produce anoutput signal .represented by the waveform 203', which signal is applied.by the OR circuit comprised of NOR circuit 209 and inverting means 210as a switch energizing signal 210 to driver means 211. Thus, switchmeans 107 is activated for a duration equal to a clock pulse durationthereby energizing the heating element included in the fuser assembly40. As may be observed from waveform 210, the activation of switch means107 for an entire clock pulseperiod during the immediately precedingclock pulse period eight and the activation of switch means 107 for aclock pulse duration during the clock pulse period 9 is sufficient tomaintain the energization of the heating element for a total timeinterval of approximately 562 milliseconds. Hence, sufficient heat isapplied to the electroscopic particles disposed in image configurationon support base 9 to fuse said particles to the support base. Thus, theprinted images derived from the successive data cards are suitably fixedto the support base to form permanent copies thereof.

means 200. It is therefore appreciated that an output signal is notproduced by any of AND gate 203, NOR circuit 204 or NOR circuit 206.However, at clock pulse 11, a print signal is applied to terminal 201and shifted into the first stage of storage means 200 as represented bywaveform 201'. At clock pulse 11, the third stage of storage means 200is occupied by the immediately preceding print signal, the fourth stageof storage means 200 is occupied by the next preceding print signal andthe seventh stage of storage means 200 is occupied by the thirdpreceding print signal. Hence, only AND gate 203 produces an outputsignal, represented by waveform 203 which, it is appreciated, admits ofa duration equal to a clock pulse duration. The signal produced by ANDgate 203 is applied as a switch energizing signal to driver means 211 bythe OR circuit comprised of NOR circuit 209 and inverting means 210 asrepresented by the waveform 210. Consequently, switch means 107 isactivated for the pre-established minimum duration to thereby energizethe heating element included in the fuser assembly 40 for acorresponding duration.

During the next succeeding clock pulse periods, the image informationrotating on the photosensitive drum is not printed and, therefore, aprint signal pulse is not applied to terminal 201, the support base 9 isnot advanced through the fuser assembly 40 and the heating elementincluded in the fuser assembly is not energized. However, at clock pulse18 image information derived from a data card and transferred to thesupport base 9 is to be fixed to the support base. Accordingly a portionof the support base upon which electroscopic particles are disposed inimage configuration is advanced to the fuser assembly 40 and aprint'signal is applied to terminal 201 and shifted into storage means200 as represented by waveform 201'. None of the second to seventhstages of storage means 200 is occupied by a print signal but theimmediately preceding print signal (i.e., the printsignal that occurredat clock pulse 11) occupies the eighth stage of the storage means.Consequently, both AND gate 203 and NOR circuit 204 produce outputsignals represented by the waveforms 203 and 204','respectively. Thesesignals are applied as a switch energizing signal to drive means 211 bythe OR circuit comprised of NOR circuit 209 and inverting means 7 210 asrepresented by the waveform 210'. Switch means 107 is thus activated fora duration equal to a clock pulse period, thereby energizing the heatingelement for a corresponding duration.

It is observed that more than six clock pulse periods (viz. seven clockpulse periods) have elapsed since the occurrence of the immediatelypreceding print signal. Also, more than six clock pulse periods haveelapsed since the termination of the immediately precedingenergization'of heating element 105. Hence, heating element 105, whichhas cooled to a lower quiescent temperature, must be energized for anadditional period of time to enable sufficient radiant energy toaccumulate in the fuser assembly 40. Thus, at clock pulse 19, theimmediately preceding print signal is shifted into the second stage ofstorage means 200 and the third through eighth stages of the storagemeans are not provided with stored print signals. Accordingly, NORcircuit 206 is activated to produce an output signal 206', admitting ofa duration equal to a clock pulse duration, which pulse is applied as aswitch energizing signal to the driver means 211 by the OR circuitcomprised of NOR circuit 209 and inverting means 210. Switch means 107is thus activated for an additional interval during clock pulse period19 to effect the required additional energization of heating element105.

At clock pulse 20 the last preceding print signal is shifted into thethird stage of storage means 200 and at clock pulse 21 another printsignal is applied to terminal 201 and shifted into storage means 200 asrepresented by the waveform 201'. It is appreciated that more than twoclock pulse periods have elapsed since the occurrence of the immediatelypreceding print signal and, in addition, more than approximately 434milliseconds have expired since the immediately preceding energizationof heating element 105 has terminated. Thus the proper fuaing of theelectroscopic particles disposed in image configuration on support base9 requires slightly more than the pre-established minimum duration ofenergization of the heating element. Consequently, at clock pulse 21 thefirst stage of storage means 200 is occupied by the print signalrepresented by waveform 201' and neither the second nor third stages ofthe storage means is occupied by a print signal. Hence, an output signalrepresented by waveform 203 is produced by AND gate 203 and an outputsignal represented by waveform 204' is produced by NOR circuit 204. TheOR circuit comprised of NOR circuit 209 and inverting means 210 respondsto the signals applied thereto to apply a switch energizing signal,represented by waveform 210' to driver means 211. Accordingly, switchmeans 107 is activated for a duration equal to a clock pulse period,thereby energizing the heating element 105 for a corresponding intervalof time.

It should now be fully appreciated from the foregoing descriptionthereof that storage means 200 stores the time related history of themovement of successive portions of support base 9 through the fuserassembly 40. Clearly, a variable time interval may elapse betweenconsecutive movements. This, of course, is represented by the selectedstages of storage means 200 which are occupied by print signals.Moreover, since the energization of the heating element of the fuserassembly is dependent upon the application of a print signal to terminal201, the selected stages of storage means 200 that are occupied by printsignals provide an indication of the length of time that has expiredbetween successive energizations of the heating element.

In the description of FIG. 3, it has been assumed that conventional,commercially available TTL logic is utilized throughout for each of theAND gates, NOR circuits, inverting means, storage means and drivermeans. However, any of the specific logic components or arrangements maybe replaced by other components or groups thereof which produce similaroutput signals in response to corresponding input conditions. Also, theprecise mode of logic operation employed thereby may differ from thatdescribed hereinabove in a matter that is obvious to those of ordinaryskill in the art. Furthermore, the logic circuit illustrated in FIG. 3may, alternatively, be implemented by MSI logic, individual circuitcomponents or MOS circuit chips. In addition, the variable supply 100illustrated in FIG. 2A may be replaced by other conventional sources ofenergy sufficient to supply the heating element with an increasedvoltage in response to a switch energizing signal produced by the ORcircuit comprised of NOR circuit 209 and inverting means 210 of FIG. 3.Accordingly, a suitable high voltage source may be selectively coupledto heating element 105 through conventional switching means, the latterbeing adapted to be activated in response to the switch energizingsignal produced by the aforementioned OR circuit. Moreover, the heatingelement 105 need not be limited merely to a conventional quartz lamp,but, alternatively, may comprise any suitable heat radiating device orother heating device conventionally utilized in fuser assemblies orother electroscopic particle fixing devices.

While the invention has been particularly shown and described withreference to an exemplary embodiment thereof, it will be obvious tothose skilled in the art that various changes and modifications in formand details may be made without departing from the spirit and scope ofthe invention. Thus, the specific numerical examples describedhereinabove are intended to be merely illustrative of the operation ofthe apparatus disclosed herein and are not intended to limit theteachings of the instant invention. Accordingly, any suitable clockpulse period and clock pulse duration may be employed herewith.Moreover, storage means 200 may comprise any conventional storage devicecapable of storing a suitable history of the previous operation of thefuser assembly and, therefore, of the intermittently moving supportbase. NOR circuit 204 may be adapted to produce an output signal ifthree or more clock pulse periods have expired since the occurrence ofthe immediately preceding print signal. Similarly, NOR circuit 206 maybe adapted to produce an output signal when any other convenient numberof clock pulse periods have expired since the occurrence of animmediately preceding print signal. And additional gating means may beprovided to produce output signals upon detecting the expiration ofother clock pulse periods. It is, of course, recognized that these NORcircuits and gating means may, therefore, produce output signalsadmitting of any desired duration to energize the heating element of thefuser assembly in accordance with the particular interval of time thathas expired since the immediately preceding energization of the heatingelement. Thus, it is intended that the appended claims be interpreted asincluding the foregoing as well as other obvious changes andmodifications.

What is claimed is:

1. Apparatus for regulating the operation of a fuser assembly inaccordance with selected information requiring the energization of saidfuser assembly wherein the radiant energy accumulated by said fuserassembly is a function of the expiration of time from an immediatelypreceding energization thereof comprising:

sensing means for sensing the occurrence of a preselected informationsignal to energize said fuser assembly for a pre-established minimumperiod of time; and

energizing means coupled to said sensing means for energizing said fuserassembly for a period of time that is dependent upon the interval oftime that has expired intermediate successive occurrences of saidpreselected information signal.

2. The apparatus of claim 1 wherein said sensing means comprises meansfor serially storing each preselected information signal and the numberof predetermined time durations separating successive ones of saidpre-selected information signals in consecutive order; and

means coupled to said storing means for generating a first energizingsignal admitting of said preestablished minimum period of time when apreselected information signal is stored in a first position of saidconsecutive order.

3. The apparatus of claim 2 wherein said energizing means comprisesmeans for generating a second energizing signal when a preselectedinformation signal is stored in a first position of said consecutiveorder and a number of predetermined time durations are stored in thenext successive positions of said consecutive order, said secondenergizing signal admitting of a period of time that is a function ofsaid number of successively stored predetermined time durations.

4. Apparatus for regulating the fusing of electroscopic particles tosuccessive portions of a support base intermittently moving through afuser assembly wherein said fuser assembly includes a source of thermalradiation coupled to a variable supply of voltage, comprising:

switch means included in said variable supply and adapted when energizedto apply an increased voltage to said source of thermal radiation fromsaid variable supply to increase the heat radiated by said sourcewhereby said electroscopic particles are fused to said support base; and

means for energizing said switch means for a period of time when aportion of said support base is moved through said fuser assembly, saidperiod of time being a function of the interval of time that has expiredsince an immediately preceding portion of said support base was movedthrough said fuser assembly.

5. The apparatus of claim 4 including storage means for storing the timerelated history of the movement of successive portions of .said supportbase through said fuser assembly, said storage means being coupled tosaid means for energizing said switch.

6. The apparatus of claim 5 wherein said storage means comprises:

shift register means including an input terminal to which is applied asignal representing the movement of a portion of said support basethrough said fuser assembly; and

means for continually shifting on a periodic basis each signal appliedto said input terminal through said shift register means whereby therelative positions occupied by signals within said shift register meansis a function of the history of the movement of said support basethrough said fuser assembly.

7. The apparatus of claim 6 wherein said means for energizing comprises:

first means for energizing said switch means for a preestablishedminimum period of time when successive portions of said support base aremoved through said. fuser assembly within a first duration;

second means for energizing said switch means for a secondpre-established period of time when a portion of said support base ismoved through said fuser assembly at a time later than the expiration ofa first interval of time after an immediately preceding portion is'moved therethrough, said second pre-established period of time beinggreater than said pre-established minimum period of time; and

third means for energizing said switch means for a third pre-establishedperiod of time when a portion of said support base is moved through saidfuser assembly at a time later than the expiration of a second period oftime after an immediately preceding portion'is moved therethrough, saidsecond interval of time being greater than said first interval of timeand said third pre-established period of time being greater than saidsecond pre-established period of time.

8. The apparatus of claim 7 wherein-said first means comprises firstgating means coupled to the first position of said shift register meansfor producing a first energizing signal admitting of a pre-establishedminimum duration when said first position is occupied by a signal.

9. The apparatus of claim 8 wherein said second means comprises secondgating means coupled to the first position of said shift register meansand to a first preselected number of successive positions of said shiftregister means for producing a second energizing signal admitting of asecond pre-established duration when said first position is occupied bya signal and none of said first preselected number of successivepositions is occupied by a signal.

10. The apparatus of claim 9 wherein said third means comprises thirdgating means coupled to the second position of said shift register meansand to a second preselected number of successive positions of said shiftregister means for producing a third energizing signal admitting of saidpre-established minimum duration when said second position isoccupied bya signal and none of said second preselected number of successivepositions is occupied by a signal.

11. The apparatus of claim 10 wherein said first, second and thirdgating means are coupled to selective gating means, said selectivegating means being adapted to produce a switch energizing signaladmitting of said pre-established minimum duration when only said firstenergizing signal is produced, said second preestablished duration whenonly said first and second energizing signals are produced and a thirdpreestablished duration when said first, second and third energizingsignals are all produced.

12. The apparatus of claim 11 wherein said variable supply includesbidirectional current conducting means supplied with an AC voltage, saidbidirectional current conducting means being initially conductive at apoint in the half cycle of said AC voltage that is a function of acontrol voltage applied thereto such that an increase in said controlvoltage tends to advance the initial conductive point and a decrease insaid control voltage tends to retard the initial conductive point, saidcontrol voltage being increased in response to theenergization of saidswitch means;

13. In combination with a heating element that is maintained at atemperature level no lower than a quiescent level of temperature, saidheating element radiating an amount of heat that is. dependent upon thelengthof time expired between successive energizations thereof,apparatus for selectively energizing said heating element for variabletime durations such that a substantially equal radiant energy level isattained thereby during each energization irrespective of the length oftime that has expired since an immediately preceding energizationthereof, comprising:

' energizing means coupled to said heating element for supplying saidheating element with energy;

storage means for storing signals representative of the history of theselective energization of said heating element;

first means coupled to said storage means and responsive to a selectiveenergizing signal for energizing said heating element for apre-established minimum duration of time when the immediately precedingenergization of said heating element occurred within a first timeduration;

second means coupled to said storage means and responsive to a selectiveenergizing signal for energizing said heating element for a secondpreestablished duration of time when a first interval of time hasexpired since the immediately preceding energization of said heatingelement, said second pre-established duration of time being greater thansaid minimum duration; and

third means coupled to said storage means and responsive to a selectiveenergizing signal for energizing said heating element for a thirdpre-established duration of time when a second interval of time hasexpired since the immediately preceding energization of said heatingelement, said third preestablished duration of time being greater thansaid second pro-established duration.

14. The combination of claim 13 wherein said storage means comprisesplural stage shift register means including an input terminal forreceiving an irregularly occurring selective energizing signal and ashift terminal for receiving a periodic shift signal, whereby thesignals applied to said input terminal are shifted through said pluralstages in timed relation such that the relative positions occupied byselective energizing signals is a function of the previous energizationsof said heating element.

15. The combination of claim 14 wherein said first, second and thirdmeans comprise first, second and third gating means coupled to selectivegating means; said first gating means including an input coupled to afirst stage of said shift register means for producing a firstenergizing signal admitting of a pre-established minimum duration when aselective energizing signal is shifted into said first stage, saidsecond gating means including an input coupled to said first stage ofsaid shift register means and inputs coupled to a first preselectednumber of successive stages of said shift register means for producing asecond energizing signal admitting of a second pre-established durationwhen a selective energizing signal is shifted into said first stage andnone of said first preselected number of successive stages receives aselective energizing signal, said third gating means including an inputcoupled to a second stage of said shift register means and inputscoupled to a second preselected number of successive stages of saidshift register means for producing a third energizing signal admittingof said pre-established minimum duration when a selective energizingsignal is shifted into said second stage and none of said secondpreselected number of successive stages receives a selective energizingsignal; and said selective gating means includes an output coupled tosaid energizing means for supplying said energizing means with a signaladmitting of said pre-established minimum duration when only said firstenergizing signal is produced, a signal admitting of said secondpre-established duration when only said first and second energizingsignals are produced and a signal admitting of said thirdpre-established duration when said first, second and third energizingsignals are all produced.

1. Apparatus for regulating the operation of a fuser assembly inaccordance with selected information requiring the energization of saidfuser assembly wherein the radiant energy accumulated by said fuserassembly is a function of the expiration of time from an immediatelypreceding energization thereof comprising: sensing means for sensing theoccurrence of a preselected information signal to energize said fuserassembly for a preestablished minimum period of time; and energizingmeans coupled to said sensing means for energizing said fuser assemblyfor a period of time that is dependent upon the interval of time thathas expired intermediate successive occurrences of said preselectedinformation signal.
 2. The apparatus of claim 1 wherein said sensingmeans comprises means for serially storing each preselected informationsignal and the number of predetermined time durations separatingsuccessive ones of said pre-selected information signals in consecutiveorder; and means coupled to said storing means for generating a firstenergizing signal admitting of said pre-established minimum period oftime when a preselected information signal is stored in a first positionof said consecutive order.
 3. The apparatus of claim 2 wherein saidenergizing means comprises means for generating a second energizingsignal when a preselected information signal is stored in a firstposition of said consecutive order and a number of predetermined timedurations are stored in the next successive positions of saidconsecutive order, said second energizing signal admitting of a periodof time that is a function of said number of successively storedpredetermined time durations.
 4. Apparatus for regulating the fusing ofelectroscopic particles to successive portions of a support baseintermittently moving through a fuser assembly wherein said fuserassembly includes a source of thermal radiation coupled to a variablesupply of voltage, comprising: switch means included in said variablesupply and adapted when energized to apply an increased voltage to saidsource of thermal radiation from said variAble supply to increase theheat radiated by said source whereby said electroscopic particles arefused to said support base; and means for energizing said switch meansfor a period of time when a portion of said support base is movedthrough said fuser assembly, said period of time being a function of theinterval of time that has expired since an immediately preceding portionof said support base was moved through said fuser assembly.
 5. Theapparatus of claim 4 including storage means for storing the timerelated history of the movement of successive portions of said supportbase through said fuser assembly, said storage means being coupled tosaid means for energizing said switch.
 6. The apparatus of claim 5wherein said storage means comprises: shift register means including aninput terminal to which is applied a signal representing the movement ofa portion of said support base through said fuser assembly; and meansfor continually shifting on a periodic basis each signal applied to saidinput terminal through said shift register means whereby the relativepositions occupied by signals within said shift register means is afunction of the history of the movement of said support base throughsaid fuser assembly.
 7. The apparatus of claim 6 wherein said means forenergizing comprises: first means for energizing said switch means for apreestablished minimum period of time when successive portions of saidsupport base are moved through said fuser assembly within a firstduration; second means for energizing said switch means for a secondpre-established period of time when a portion of said support base ismoved through said fuser assembly at a time later than the expiration ofa first interval of time after an immediately preceding portion is movedtherethrough, said second pre-established period of time being greaterthan said pre-established minimum period of time; and third means forenergizing said switch means for a third pre-established period of timewhen a portion of said support base is moved through said fuser assemblyat a time later than the expiration of a second period of time after animmediately preceding portion is moved therethrough, said secondinterval of time being greater than said first interval of time and saidthird pre-established period of time being greater than said secondpre-established period of time.
 8. The apparatus of claim 7 wherein saidfirst means comprises first gating means coupled to the first positionof said shift register means for producing a first energizing signaladmitting of a pre-established minimum duration when said first positionis occupied by a signal.
 9. The apparatus of claim 8 wherein said secondmeans comprises second gating means coupled to the first position ofsaid shift register means and to a first preselected number ofsuccessive positions of said shift register means for producing a secondenergizing signal admitting of a second pre-established duration whensaid first position is occupied by a signal and none of said firstpreselected number of successive positions is occupied by a signal. 10.The apparatus of claim 9 wherein said third means comprises third gatingmeans coupled to the second position of said shift register means and toa second preselected number of successive positions of said shiftregister means for producing a third energizing signal admitting of saidpre-established minimum duration when said second position is occupiedby a signal and none of said second preselected number of successivepositions is occupied by a signal.
 11. The apparatus of claim 10 whereinsaid first, second and third gating means are coupled to selectivegating means, said selective gating means being adapted to produce aswitch energizing signal admitting of said pre-established minimumduration when only said first energizing signal is produced, said secondpre-established duration when only said first and second energizingsignals are produced and a third pre-Established duration when saidfirst, second and third energizing signals are all produced.
 12. Theapparatus of claim 11 wherein said variable supply includesbidirectional current conducting means supplied with an AC voltage, saidbidirectional current conducting means being initially conductive at apoint in the half cycle of said AC voltage that is a function of acontrol voltage applied thereto such that an increase in said controlvoltage tends to advance the initial conductive point and a decrease insaid control voltage tends to retard the initial conductive point, saidcontrol voltage being increased in response to the energization of saidswitch means.
 13. In combination with a heating element that ismaintained at a temperature level no lower than a quiescent level oftemperature, said heating element radiating an amount of heat that isdependent upon the length of time expired between successiveenergizations thereof, apparatus for selectively energizing said heatingelement for variable time durations such that a substantially equalradiant energy level is attained thereby during each energizationirrespective of the length of time that has expired since an immediatelypreceding energization thereof, comprising: energizing means coupled tosaid heating element for supplying said heating element with energy;storage means for storing signals representative of the history of theselective energization of said heating element; first means coupled tosaid storage means and responsive to a selective energizing signal forenergizing said heating element for a pre-established minimum durationof time when the immediately preceding energization of said heatingelement occurred within a first time duration; second means coupled tosaid storage means and responsive to a selective energizing signal forenergizing said heating element for a second pre-established duration oftime when a first interval of time has expired since the immediatelypreceding energization of said heating element, said secondpre-established duration of time being greater than said minimumduration; and third means coupled to said storage means and responsiveto a selective energizing signal for energizing said heating element fora third pre-established duration of time when a second interval of timehas expired since the immediately preceding energization of said heatingelement, said third pre-established duration of time being greater thansaid second pre-established duration.
 14. The combination of claim 13wherein said storage means comprises plural stage shift register meansincluding an input terminal for receiving an irregularly occurringselective energizing signal and a shift terminal for receiving aperiodic shift signal, whereby the signals applied to said inputterminal are shifted through said plural stages in timed relation suchthat the relative positions occupied by selective energizing signals isa function of the previous energizations of said heating element. 15.The combination of claim 14 wherein said first, second and third meanscomprise first, second and third gating means coupled to selectivegating means; said first gating means including an input coupled to afirst stage of said shift register means for producing a firstenergizing signal admitting of a pre-established minimum duration when aselective energizing signal is shifted into said first stage, saidsecond gating means including an input coupled to said first stage ofsaid shift register means and inputs coupled to a first preselectednumber of successive stages of said shift register means for producing asecond energizing signal admitting of a second pre-established durationwhen a selective energizing signal is shifted into said first stage andnone of said first preselected number of successive stages receives aselective energizing signal, said third gating means including an inputcoupled to a second stage of said shift register means and inputscoupled to a second preselected number of successive stages of saidshift register means for producing a third energizing signal admittingof said pre-established minimum duration when a selective energizingsignal is shifted into said second stage and none of said secondpreselected number of successive stages receives a selective energizingsignal; and said selective gating means includes an output coupled tosaid energizing means for supplying said energizing means with a signaladmitting of said pre-established minimum duration when only said firstenergizing signal is produced, a signal admitting of said secondpre-established duration when only said first and second energizingsignals are produced and a signal admitting of said thirdpre-established duration when said first, second and third energizingsignals are all produced.